The present invention relates to a single crystal pulling apparatus for growing and pulling up a single crystal ingot from a molten polycrystal substance in accordance with the Czochralski (CZ) method.
The single crystal pulling apparatus of this kind comprises a main chamber wherein the single crystal is grown, and in this main chamber are housed a crucible for containing the polycrystal substance such as silicon and a heater arranged to surround the crucible. The heater is for heating and melting down the polycrystal substance in the crucible. Beneath the main chamber are provided mechanisms for rotating the crucible about the center line thereof to control the uniformity of the heat flux in the molten polycrystal substance during the crystal growing operation. Rising above the main chamber is a towering structure of a crystal pull chamber which is an upright, substantially cylindrical enclosure terminating in an upper structure of a crystal pulling mechanism containing a winder assembly. An isolation valve is provided between the main chamber and the pull chamber.
In such single crystal pulling apparatus, the single crystal is caused to grow from the lower tip of a seed crystal which is attached to the lower end of a pull device such as a wire suspended from the winder assembly and which is dipped in a polycrystal substance that is melted down in the crucible. As the pull wire together with the seed crystal is rotated and drawn up higher at a predetermined velocity, the desired single crystal is grown longer from the tip of the seed crystal. At the beginning of the single crystal pulling operation, the isolation valve is opened to thereby render the main chamber and the pull chamber into communication. Then, the air is drawn out of these chambers by means of a vacuum pump, and an inert gas such as argon is supplied to the chambers. Thus, the single crystal pulling operation is carried out in this inert gas atmosphere. When the single crystal pulling operation is completed, the single crystal ingot is brought up into the pull chamber, and after the isolation valve is closed to thereby interrupt the communication between the two chambers, the single crystal ingot is removed from the pull chamber.
In order to maintain the stability of the operation, as well as to obtain defectless single crystal, the wire and the crucible shaft (or more particularly the center line of the crucible) are aligned to be collinear with each other. It must be carefully observed that the wire does not depart substantially from the center line of the crucible.
(Problems the Invention seeks to solve)
However, in the conventional single crystal pulling apparatus, the crystal pulling mechanism containing the winder assembly is attached integrally and rigidly to the top portion of the pull chamber so that when the air in the main chamber is drawn by the vacuum pump and the main chamber is heated, the main chamber is deformed, and this causes the pull chamber to ascend, descend and/or tilt more or less whereby the winder assembly is displaced from its original proper position and the wire is shifted away from the center line of the crucible. When this occurs, the wire swirls, the seed crystal fails to stand vertically, and the crystal grows cranked and many other defects occur in the growing crystal.
Also, when the crystal pulling mechanism containing the winder assembly is attached integrally and rigidly to the pull chamber, the vibration created by the drive system of the winder assembly is propagated unmitigatedly to the pull chamber and the main chamber whereby the molten crystal in the crucible is rippled and the normal growth of the single crystal is affected.
The present invention was contrived in view of the above problems and it is, therefore, an object of the invention to provide a single crystal pulling apparatus which is designed such that the wire to draw up the single crystal is always kept aligned collinearly with the center axis (that is, the axis of rotation) of the crucible even when the main chamber is deformed by heat or otherwise, and also such that the vibration of the winder assembly is not propagated to the pull chamber, let alone the main chamber, so that the single crystal grown in it will have scarce defect and the single crystal pulling operation proceeds stably and dependably.